Process for Removal of the Catalytic Coating Material from Spent, Defective or Unused Metal Support Catalytic Converters

ABSTRACT

Process for recovering catalytic coating material from catalytic converters, catalytic material or catalytic assemblies where the catalytic coating material is bonded to a metal supporting structure, the process being carried out by contacting the catalytic coating material with nitric acid and/or a nitrate-containing chemical or material, applying heat, agitating the catalytic converters, catalytic material or catalytic assemblies being processed to dislodge the catalytic coating material, and rinsing the catalytic converters, catalytic material or catalytic assemblies with water to facilitate the removal of remaining catalytic coating material, and recovering ionic metal species dissolved by the nitric acid and/or nitrate-containing chemical or material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional application Ser. No. 60/560,114, filed on Apr. 7, 2004, the complete disclosure of which is incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to destruction of the bonding between a catalyst coating material and its underlying metal support structure, and subsequent removal of the catalyst material from spent, defective, or unused metal support catalytic converters.

2. Background of the Invention

Metal support catalytic converters or converter assemblies, also commonly known as steel mantle catalytic converters, metal substrate catalytic converters, are often used to reduce air pollution emissions. In particular, some examples of their use is in connection with mobiles and stationary internal combustion engines, such as those in automobiles and power generators. Catalytic crackers, which also contain catalytic materials, are often used in the petroleum refining industry. In addition there are other applications which employ the use of catalytic coating material containing valuable metals which are fixed to a metal support structure.

The valuable catalytic materials remain behind when the catalytic, converter or other device containing the catalytic coating materials is removed from service. In addition, defective converters which cannot be used contain these valuable metals, as do unused converters, which for one or more reasons, may not have been used, and may no longer be useful for the purpose for which they were manufactured. Valuable catalytic metals present in the coatings of converters may include precious metals, and for example, are often be left behind in spent, defective or unused catalytic converters or devices.

A need exists for an improved process for removing metal containing coatings from a supporting metal structure, and in particular where the coating contains a precious metal and other metals such as nickel, and where the supporting metal structure comprises a steel structure

SUMMARY OF THE INVENTION

The invention provides a process for recovering catalytic coating material from catalytic converters, catalytic material or catalytic assemblies where the catalytic coating material is bonded to a metal supporting structure, the process being carried out by contacting the catalytic coating material with nitric acid and/or a nitrate-containing chemical or material, applying heat, agitating the catalytic converters, catalytic material or catalytic assemblies being processed to dislodge the catalytic coating material, and rinsing the catalytic converters, catalytic material or catalytic assemblies with water to facilitate the removal of remaining catalytic coating material, and removing ionic metal species present in the solution with a recovery step.

The invention provides an economical process for removing metal containing coatings from a supporting metal structure, and in particular where the coating contains a precious metal and other metals such as nickel. The process may be used for removal of metal catalytic coatings from a steel structure.

The invention is economically advantageous in that relatively inexpensive nitric acid may be employed to facilitate the removal of the coatings from a metal structure.

The invention, in addition to being economically advantageous, has significant environmental advantages, since the process seeks to avoid the release of heavy metals in any form as well as employ the use of chemicals which may be severely toxic to the environment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Description/Specification of the Invention

The invention provides a process Whereby the bond that fixes the catalyst coating material containing any combination of platinum group metals and other elements onto the underlying metal support structure of metal support catalytic converters is destroyed or broken and the said catalytic coating material is subsequently removed from its support structure for recycling of the valuable metals contained in the coating material. The removal process of separating the catalytic coating material from the metal support structure of spent, defective or unused metal support catalytic converters or converter assemblies, also commonly known as steel mantle catalytic converters, metal substrate catalytic converters, or other terms, is then accomplished by a suitable removal step, which may, for example, comprise ultrasonic agitation, a simple rinse using a liquid such as water, the use of some other mechanical means, or a combination of any one or more of these. These converters and converter assemblies are primarily used to reduce air pollution emissions of mobile and stationary internal combustion engines such as those in automobiles and power generators. In addition, the process may also be applicable for catalytic crackers used in the petroleum refining industry and other applications where catalytic coating material containing valuable metals are fixed to a metal support structure.

The process according to the present invention is accomplished by effecting contact between the catalytic coating material contained in or on the metal support catalytic converters and nitric acid and/or a nitrate-containing chemical or material (that is any chemical or compound which is classified as a nitrate by its material safety data sheet or containing a chemical or material so classified) of a minimum of 0.1% nitric acid or 1% nitrate content by weight. The nitric acid and/or nitrate-containing chemical or material is put in contact with the catalyst coating material to destroy the bonding between the catalyst coating material and the underlying metal structure. Once the bonding is destroyed, the catalyst coating material is removed by either ultrasonic agitation, a simple liquid rinse, or mechanical agitation preferably while immersed in a mild detergent solution, or through the application of a pressure spray. The contact described above can be effected by one or more of gaseous, liquid or solid means, including a combination thereof, whereby a nitrate-containing chemical or material is either heated in conjunction with the metal support catalytic converters being processed at temperatures ranging between 0 C and the melting point of die underlying metal structure of said metal support catalytic converters, or one or more of the components are heated separately. Preferably, the temperature range for the step of contacting the catalyst coating material with the nitric acid and/or nitrate-containing chemical or material is carried out at a temperature range of between approximately 65 C and the melting point of the underlying metal structure.

There are many possible implementations of the invention, but excellent results have been achieved by immersing the catalytic converters, catalytic material or catalytic assemblies in nitric acid and/or a nitrate-containing chemical or material solution in a stainless steel ultrasonic tank and using ultrasonic agitation to facilitate the destruction of the bonding and removal of the catalyst coating material from its underlying metal support structure. In the above implementation, the nitric acid and/or nitrate-containing material may be provided in a solution of 60% water and 40% nitric acid solution, with the initial nitric acid solution consisting of 68% nitric acid and 32% water and it is preferred that the ultrasonic tank solution be kept at a temperature of between approximately 65 C and 100 C during agitation. For example, the material being agitated in the tank may be placed in a stainless steel basket, which, on a regular basis, may be removed from the tank for inspection of the material being processed to check on the progress of catalytic coating material removal. In a powerful ultrasonic tank and with catalytic converter material that has had external casings or other extraneous structure removed, the agitation time required to destroy the bonding between the catalyst coating material and the underlying metal support structure and remove the valuable catalytic coating material may be very short in duration. In order to facilitate the progress of the process, the structure and material of the catalytic converters, catalytic material or catalytic assemblies that no longer have valuable catalytic coating material affixed to it may be removed prior to or during the process.

After a suitable agitation time, the catalytic converters, catalytic material or catalytic assemblies are then taken from the ultrasonic tank with virtually all catalytic coating material having been removed. Typically, a light water rinse is applied in another, tank to the catalytic converters, catalytic material or catalytic assemblies being taken from the ultrasonic tank to wash off any catalytic coating material that remains adhered by surface tension.

The use of a tank containing a nitric acid and/or nitrate-containing solution to carry out the step of contacting the catalytic converters, catalytic material or catalytic assemblies may enable repeated use of the solution. Once the initial catalytic converters, catalytic material or catalytic assemblies have been removed from the ultrasonic tank, the ultrasonic tank is then ready to receive more converters or converter material for agitation and removal of any affixed catalytic coating material. This process can be continued until either the nitric acid has lost its effectiveness or the sheer mass of loose catalytic coating material removed from its underlying metal support structure begins to interfere with the agitation and removal process in the ultrasonic tank. If the nitric acid has been consumed, fresh nitric acid can be added to the ultrasonic tank; however, if a great deal of catalytic coating material has accumulated in the tank, it is preferable to drain and filter the tank contents to capture and remove the valuable catalytic coating material. The filtered solution can then be returned to the ultrasonic tank to process more converter material.

One advantage of the invention is that unlike acid leech chemistry such as aqua regia, with this process very little iron is leached into solution from the metal support structure of the converters or converter assemblies, which in all current implementations are steel alloys resistant to nitric acid. However, because of the hot nitric acid solution present in the ultrasonic tank some of the metals in the catalyst coating material, including, but not limited to, palladium may be dissolved into solution. These ionic metal species can be readily converted to solid form and removed from solution by a recovery step. The recovery step may be carried out using electrowinning, electrolytic precipitation, precipitation with chemicals or other known techniques. Some of the techniques mentioned above would require that the ultrasonic tank solution be chemically modified such that it could not be reused for processing converter material and a fresh tardy solution of water and nitric acid would have to be prepared for the ultrasonic tank. In those instances, for the sale of economy, the ultrasonic tank solution preferably may be used until it is so impregnated with ionic species that it can no longer effectively destroy the bonding between the catalytic coating material and the underlying metal support structure.

The invention described above has been found to be simple, extremely economical and is highly effective in destroying the bonding between the catalyst coating material and the underlying metal support structure in all types of metal support catalysts currently in use for reduction of air pollutants from internal combustion engines. This breaking of the bonding allows for easy removal of the valuable spent, defective or unused catalyst coating material and subsequent recovery of the platinum group metals, nickel and other metals that may be contained in the catalyst coating material. In addition, the invention may also be effective in recovery of valuable metals from other catalyst material and in other recovery applications. Furthermore, the invention has significant cost and environmental advantages in that relatively inexpensive nitric acid is the principal process chemical and there is neither any release of heavy metals in any form nor any use of toxic chemicals.

While the invention has been described with reference to specific embodiments, the description is illustrative and is not to be construed as limiting the scope of the invention. Various modifications and changes may occur to those skilled in the art without departing from the spirit and scope of the invention described herein and as defined by the appended claims. 

1. A process for recovering catalytic coating material from catalytic converters, catalytic material or catalytic assemblies where the catalytic coating material is bonded to a metal supporting structure, the method comprising the steps of: a) contacting the catalytic coating material supported on a metal supporting structure of a catalytic converter assembly with nitric acid and/or a nitrate-containing chemical or material for a sufficient period of time to destroy bonds between the catalytic coating material and the metal supporting structure; b) removing catalytic coating material from the supporting structure.
 2. The process of claim 1, wherein the step of removing catalytic coating material comprises ultrasonic agitation.
 3. The process of claim 1, wherein the step of removing catalytic coating material comprises subjecting the catalytic coating material to a rinse with a liquid.
 4. The process of claim 3, wherein the rinse liquid comprises water.
 5. The process of claim 1, wherein the step of removing catalytic coating material comprises immersing the catalytic coating material in a detergent solution and agitating the solution.
 6. The process of claim 1, wherein the step of removing catalytic coating material comprises subjecting the catalytic coating material to a pressurized stream of liquid.
 7. The process of claim 6, wherein the liquid of the pressurized stream comprises water.
 8. The process of claim 1, wherein the step of contacting the catalytic coating material supported on a metal supporting structure of a catalytic converter assembly with a nitrate-containing chemical or material is done at temperatures ranging from about 0 C to about the melting point of the metal supporting structure.
 9. The process of claim 1, wherein the step of contacting the catalytic coating material supported on a metal supporting structure of a catalytic converter assembly with nitric acid and/or a nitrate-containing chemical or material is done at temperatures ranging from about 65 C to 100 C.
 10. The process of claim 1, wherein the nitric acid and/or nitrate-containing material is supplied in the form of a gaseous phase.
 11. The process of claim 1, wherein the nitric acid and/or nitrate-containing material is supplied in the form of a solid phase.
 12. The process of claim 1, wherein the nitric acid and/or nitrate-containing material is supplied in the form of a liquid phase.
 13. The process of claim 12, including the step of recovering dissolved ionic metal species in the liquid phase.
 14. The process of claim 13, wherein the step of recovering dissolved ionic metal species present in the liquid phase comprises electronically collecting the ionic metal species, precipitating the ionic metal species out of the solution, or a combination of both.
 15. The process of claim 1, wherein the nitric acid and/or nitrate-containing material is supplied in the form of one or more of a liquid phase, a solid phase, a gaseous phase, or a combination thereof.
 16. The process of claim 1, wherein the nitric acid and/or nitrate-containing solution comprises a solution of about 60% water and about 40% nitric acid solution, with the initial nitric acid solution consisting of about 68% nitric acid and about 32% water.
 17. The process of claim 1, further comprising the step of removing structure from the catalytic converters, catalytic material or catalytic assemblies which does not have catalytic coating material affixed to it.
 18. The process of claim 1, wherein the nitric acid and/or nitrate-containing material is confined in a tank, and wherein the catalytic converters, catalytic material or catalytic assemblies are immersed in the tank.
 19. The process of claim 18, wherein the tank is an ultrasonic tank, and the step of contacting the catalytic coating material supported on a metal supporting structure of a catalytic converter assembly with a nitric acid and/or nitrate-containing chemical or material comprises agitating the catalytic converters, catalytic material or catalytic assemblies while they are immersed in the tank.
 20. The process of claim 1, wherein the nitric acid and/or nitrate-containing material comprises a minimum of 1% nitrate content by weight.
 21. The process of claim 1, wherein the step of contacting the catalytic coating material supported on a metal supporting structure of a catalytic converter assembly with nitric acid and/or a nitrate-containing chemical or material is carried out with the further step of applying heat.
 22. The process of claim 21, wherein the heat is applied to maintain the temperature of the nitric acid and/or nitrate-containing chemical or material at about 65 C to 100 C.
 23. The process of claim 18, including the step of agitating the nitric acid and/or nitrate-containing material in the tank to dislodge the catalytic coating material.
 24. The process of claim 23, including the step of removing the catalytic converters, catalytic material or catalytic assemblies from the tail, and contacting the catalytic converters, catalytic material or catalytic assemblies with a liquid rinse to facilitate the removal of catalytic coating material remaining which was not separated from the catalytic converters, catalytic material or catalytic assemblies during the agitation step.
 25. A process for recovering platinum group metals and other metals such as nickel from catalytic converters, catalytic material or catalytic assemblies where the catalytic coating material is bonded to a metal supporting structure, the method comprising the steps of: a) contacting the catalytic coating material supported on a metal supporting structure of a catalytic converter assembly with nitric acid and/or a nitrate-containing chemical or material for a sufficient period of time to destroy bonds between the catalytic coating material and the metal supporting structure; b) removing catalytic coating material from the supporting structure. 